Fix reproxy start if use_reclient is not set or found

If use_reclient_value.py is not found and args.gn only has
use_remotexec=true, the autoninja fails to start reproxy.

Change-Id: I6608ea48b66864bf2ab89176b6b01a79e07b7564
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6059221
Reviewed-by: Fumitoshi Ukai <ukai@google.com>
Commit-Queue: Aleksei Khoroshilov <akhoroshilov@brave.com>

autoninja.py

@@ -261,6 +261,8 @@ def _main_inner(input_args, build_id, should_collect_logs=False):
                 assert use_reclient != True
                 use_reclient = False
                 continue
+        if use_reclient is None:
+            use_reclient = use_remoteexec
 
         if use_remoteexec:
             if use_reclient: